A stunning light display over Saturn has stumped scientists who sayit behaves unlike any other planetary aurora known in our solar system.The blueish-green glow was found over the ringed planet's north polar region just like Earth's northern lights.It was discovered by the infrared instruments on NASA's Cassini spacecraft.'We've never seen an aurora like this elsewhere,' said Tom Stallard,a scientist working with Cassini data at the University of Leicester.'Thisaurora covers an enormous area across the pole. Our current ideas onwhat forms Saturn's aurora predict that this region should be empty, sofinding such a bright aurora here is a fantastic surprise.'

Auroras are caused by charged particles streaming along the magnetic field lines of a planet into its atmosphere.Particles from the sun cause Earth's auroras. Many, but not all, of theauroras at Jupiter and Saturn are caused by particles trapped withinthe magnetic environments of those planets.Jupiter's main auroral ring is caused by interactions in Jupiter'smagnetic environment and remains constant in size. Saturn's main aurorais caused by the solar wind, and changes size dramatically as the windvaries. However, the newly observed aurora at Saturn doesn't fit intoeither category.The new infrared aurora appears in a regionhidden from NASA's Hubble Space Telescope. Cassini observed it when thespacecraft flew near Saturn's polar region. In infraredlight, the aurora sometimes fills the region from around 82 degreesnorth all the way over the pole. This new aurora is also constantlychanging, even disappearing within a 45 minute-period. 'There issomething special and unforeseen about this planet's magnetosphere andthe way it interacts with the solar wind and the planet's atmosphere,'Cassini scientist Nick Achilleos from the University College Londonsaid.The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.